Hi Josh ,
I have talked to the team regarding your concern. There were actually two opinions and I can not deny that your point is valid to some extent. Indeed the current implementation includes the invisible columns in the count.
From a programmers point of view - this is the count of the columns in a collection regardless of their visual state . Additionally the state can be changed runtime - e.g .turn the visibility on and off. In such case we do not have to explicitly take care of the frozen columns count as well ( e.g. change it with the count of columns shown or hidden).
The result is - we have intuitive API for coders and introduce some confusion for end users in scenario like yours.
Most of the team were negative about changing the logic to exclude hidden columns from count as this would introduce some breaking changes to the existing codebase of many of our clients.
the Telerik team